1. Field of the Invention
The invention relates to a method for controlling a quantity of medium transferable between two rollers, such as from a screen roller of a printing machine onto a roller in contact with the screen roller.
So-called short inking units, such as anilox inking units, for example, which are installed in printing machines, have become known heretofore from the published German Patent Document DE 198 40 613 A1. They comprise a screen roller, also known as an anilox roller, which is formed on the circumference thereof with depressions capable of being filled with ink or varnish. The screen roller has a chambered doctor blade assigned thereto which wipes or scrapes the ink or varnish off the screen roller. The screen roller co-operates with an ink applicator roller, onto which a constant quantity of ink/varnish is transferred due to the depressions. In the event of an increase in the printing and machine speed, respectively, a slight decrease in the ink density measured on a print carrier occurs because of the normally high-viscosity offset ink. This may result from the fact that the depressions are no longer filled correctly at higher printing speeds, because the depressions are no longer emptied so effectively upon contact with the ink applicator roller or because the transfer of ink from the screen roller onto the ink applicator roller and, via a plate cylinder, onto a blanket cylinder and from the latter onto the print carrier is impaired.
In order to have an effect upon the printed ink density, also called the optical density, in anilox inking units, it has become known heretofore to exert an influence upon the slip between the screen roller and the ink applicator roller. When the two rollers have the same circumferential speeds, i.e., there is no slip, an optimum transfer of ink from the screen roller onto the ink applicator roller takes place. When slip occurs between these rollers, the printed ink density decreases due to the diminishing ink quantity transferred from the screen roller onto the ink applicator roller.
It has become known from the hereinaforementioned published German Patent Document DE 198 40 613 A1 that it is unimportant whether the slip is positive or negative, and that only the absolute size thereof is critical. By an adjustment of the slip, therefore, the printed ink density can be changed relatively quickly.